The behavior and physiological actions of the fungicide chlorothalonil in upland soil

The present study was undertaken in order to clarify the behavior and physiological actions of chlorothalonil (tetrachloroisophthalonitrile, a major fungicide in Japan) in upland soil. In addition, the physicochemical and physiological properties of chlorothalonil were compared with those of other chemicals as controls. 1. Measurement of chlorothalonil leaching using the pan lysimeter method on a sandy upland field. The extent of chlorothalonil leaching was measured by using the pan lysimeter method on a sandy upland field. A collecting pan (30 x 30 cm) in the lysimeter was installed into the soil profile horizontally at 50 cm below the soil surface. The total volume of leachate and its ratio to the total rainfall during the monitoring period (125 days) were 608.2 mm and 65%, respectively. The test chemicals were chlorothalonil, simazine, diazinon, metolachlor, dimethoate and Clsup(-) as a tracer. Chlorothalonil, diazinon and metolachlor were not detected in the leachate. The maximum concentrations of dimethoate and simazine were 18.4 ppb and 1.0 ppb, respectively. During the monitoring period, the total mass of pesticide leaching and its ratio to the application rate for dimethoate were 2.99 mg/square m and 3.5%, respectively. The corresponding values for simazine were 0.33 mg/square m and 0.4%, respectively. 2. Carbon isotope fractionation during chlorothalonil dissipation in an upland soil. A change in the standing of the deltasup(13)C value of a pesticide during its dissipation in an upland soil was investigated. Chlorothalonil as a test chemical was added to the soil (light-colored Andosol) and incubated at 30degC in the dark. The deltasup(13)C value of chlorothalonil in the soil increased from -26.5 to -22.5 permille during the incubation period of 70 days. The enrichment factor in this study was -2.6 permille. These results suggest the occurrence of carbon isotope fractionation during the dissipation of chlorothalonil in the soil environment.